The present invention relates to automatic control apparatus for a heat pump system. In particular, it relates to apparatus which will serve in a dual manner either to operate the heat pump system in an energy saving mode, useful as a standby mode of operation when selected by the user, or to automatically switch the heat pump system into such a standby mode whenever certain predetermined conditions occur.
The basic functional operating modes for a heat pump system are HEAT and COOL during which the refrigerant compressor is operated to enable the heat exchange function to occur. The user-operated mode selection switch is generally included with the room thermostat control which is used to set the target temperature at which the room or other conditioned space is desired to be maintained, typically 72.degree. F.
When the conditioned space is unoccupied, as for example when a resident is away on vacation, the resident may prefer to reset the thermostat for a new target temperature, such as 55.degree. F. in the winter or 85.degree. F. in the summer, so as to conserve energy and reduce the utility bill when it is not necessary to maintain temperatures at the normal 72.degree. F. level.
In the past, electromechanical controls have been commonly employed as the heat pump control system. These have comprised simple switches, thermostatic sensors, meter type readout devices, and also, in some cases, electromechanical clock timers for such things as night-time temperature set-back controls. Although these electromechanical devices are adequate for the simple control they afford, there is a need for more sophisticated controls that will automatically adjust to different target temperatures in response to changing conditions. This could be as a convenience to the user, as where the conditioned space is vacant for long periods of time spanning hot and cold seasons, or could serve as a fail-safe device that would take over in the case of a defect occurring in the system.